US Army experts have determined the wound cavity volume created in vital organs by an expanding hunting bullet is the sole basis of its lethality, as determined by time to death. Quite simply, a bullet that creates a greater wound cavity volume results in a shorter time to death.

Common expanding hunting bullet performance metrics, such as impact energy, weight retained, mushroom diameter, and sectional density, are inapplicable or badly misleading when used to either predict or evaluate an expanding hunting bullet’s lethality in terms of actual field wounding. The reason is these metrics focus on the bullet, not the wound cavity modeled and measured in a test medium, such as gel, nor an actual wound cavity observed and measured in an animal. Data-based articles explaining why can be accessed by clicking on the “Table of Content” link below.

Guppy metrics, found by clicking on the “Guppy Model” tab on this website’s header, and their mathematical definitions, found by clicking on the “Guppy Tech” tab, represent engineering-based terminal performance concepts embedded in the simulated wound cavity created in synthetic gel by an expanding hunting bullet. Field and skinning-shed data from a 2023 zebra management hunt show that Guppy metrics and their values obtained from gel-tested bullets are empirically linked to actual field performance because they focus on the wound cavity modeled in the gel rather than the post-test characteristics of the bullet. These terminal performance concepts, the Guppy model, and ways to apply Guppy metrics are discussed in articles that can be accessed by clicking on the “Table of Contents” link below.

Guppy metrics are typically not available unless individuals perform their own gel tests on candidate bullets. However, personal gel testing and management hunt data have shown the magnitudes of Guppy metrics can be related to a bullet’s general (generic) design. These general relationships can be used in conjunction with a simple, personally-derived empirical equation to strategically select both a cartridge and a cartridge’s specific bullet based on hunt circumstances. A three-part article with worked example problems is presented that demonstrates such applications, accessed by clicking on the “Table of Contents” link below.

Clicking on the “Terminal Performance Album” link below provides photos of the actual wounding that can be produced in vital organs by an expanding hunting bullet. The photos also indicate the variety of autopsy observations required to both critically and realistically evaluate a bullet’s actual field performance.  Reading the 2023 zebra management hunt report, accessed by clicking on the “2023 Hunt Report” tab on this website’s header, will provide the context and explanations for the critical wounding aspects being depicted.  

This website is frequently updated with new terminal performance articles. Please periodically check this page for new content.